Gate driver for power device

ABSTRACT

A power module includes a power semiconductor device having a first terminal, a second terminal, and a third terminal. The second terminal is a control terminal to regulate flow of electricity between the first and third terminals. A gate driver has an output node coupled to the second terminal of the power device. The gate driver is configured to output a first conductive state, a second conductive state, and a third conductive state. A pull-down resistor has a first end and a second end. The first end of the pull-down resistor is coupled to the output of the gate driver.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 60/288,667, filed on May 4, 2001, which is incorporated by reference herein for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to a gate driver for power semiconductor devices.

Many low voltage electronic circuits, e.g., MOSFET devices, are used to drive high voltage switching transistors, e.g., power MOSFETs, insulated gate bipolar transistor devices (IGBTs), gate controlled thyristors, and the like. A power semiconductor switch or device is switched from a nonconducting state to a conducting state by raising the gate-source voltage from below to above a threshold voltage.

One or more low voltage transistors, coupled to an output node of the gate driver, apply appropriate voltages to the gate or control terminal of the power device to turn on or turn off the power device. When the power device is an N-channel metal oxide semiconductor field effect transistor (NMOSFET), the device is turned on by applying a high voltage to the gate of the power switch and turned off by applying a low voltage to the gate. In contrast, if the power device is a P-channel metal oxide semiconductor field effect transistor (PMOSFET), the device is turned on by applying a low voltage to the gate of the power switch and turned off by applying a high voltage to the gate.

Circuitry of the gate driver may be configured a number of different ways. In one common configuration, the gate driver includes two transistors, i.e., upper and lower transistors, connected in series in a half bridge configuration. The upper transistor is a P-type transistor, such as a PMOSFET or PNP bipolar transistor. The lower transistor is an N-type transistor, such an NMOSFET or NPN bipolar transistor. An output node of the gate driver is coupled to a node between the two transistors to output and apply a high or low potential to the gate of the power switch according to the conductive states of the two transistors in series.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, a power module includes a power semiconductor device having a first terminal, a second terminal, and a third terminal. The second terminal is a control terminal to regulate flow of electricity between the first and third terminals. A gate driver has an output node coupled to the second terminal of the power device. The gate driver is configured to output a first conductive state, a second conductive state, and a third conductive state. A pull-down resistor has a first end and a second end. The first end of the pull-down resistor is coupled to the output node of the gate driver.

In another embodiment, a gate driver for a power semiconductor device includes an output node to apply a first electrical state, a second electrical state, and a third electrical state to the power semiconductor device. A first input node receives a first input signal or a second input signal. A second input node receives an enable signal or a disable signal. The output node of the gate driver is at the third electrical state if the disable signal is received at the second input node regardless of any signal received at the first input node. The output node of the gate driver is at the first electrical state if the enable signal is received at the second input node and the first input signal is received at the first input node. The output node of the gate driver is at the second electrical state if the enable signal is received at the second input node and the second input signal is received at the first input node.

In yet another embodiment, a gate driver for a power semiconductor device includes an output node to apply a first electrical state, a second electrical state, and a third electrical state to the power semiconductor device. A first input node receives a first input signal or a second input signal. A second input node receives an enable signal or a disable signal. A P-type transistor has a terminal coupled to the output node of the gate driver. An N-type transistor has a terminal coupled to the output node of the gate driver. The disable signal received at the second input node turns off the fist and second transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic diagram of a conventional power module having a gate driver and a power semiconductor device.

FIG. 2 illustrates a schematic diagram of a conventional gate driver for a power semiconductor device.

FIG. 3 illustrates a schematic diagram of a power module having a gate driver and a power semiconductor device according to one embodiment of the present invention.

FIG. 4 illustrates a schematic diagram of a gate driver for a power semiconductor device according to one embodiment of the present invention.

FIG. 5 illustrates a schematic diagram of a gate driver for a power semiconductor device according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention relate to a gate driver for a power semiconductor switch or device as well as a power module having a gate driver and a power semiconductor device. In one embodiment, a gate driver has a tri-state output: a first state (turn-on state) that outputs a high voltage, a second state (turn-off state) that outputs a low voltage, and a third state (high impedance state) that places the gate driver at a high impedance state. The high impedance state may be used to turn off the power device slowly during occurrences of sudden current spikes to prevent device damages. In one embodiment, the gate driver has an input node to place the gate driver in a high impedance state according to the signals received.

Referring to FIG. 1, a conventional power module 50 includes a power semiconductor switch or device 52, e.g., a power MOSFET, having a first terminal coupled to a high voltage source, a second or control terminal coupled to an output node of a gate driver, and a third terminal coupled to a low voltage source or ground. As used herein, a second terminal of a transistor generally refers to a control terminal such as a gate, that regulates the electrical current flow between the other two terminals of the device. Accordingly, the two terms “second terminal” and “control terminal” are used interchangeably when used in connection with a transistor.

A load 54, represented by an inductor L1 and a resistor R1, is coupled to the first terminal, e.g., a drain electrode, of the switch 52. One end of a resistor R2 is coupled to the second terminal of the switch, while the other end is coupled to an output node of a gate driver, as described below. The resistor R2 generally has a relatively low resistance and is provided to control the turn-on or turn-off speed of the switch. A resistor R3 is coupled to the third terminal, e.g., a source electrode, and to a low voltage source or ground. A sense node 58, provided between the third terminal and the resistor R3, is coupled to a comparator 70, to enable detection of any unusual current spikes and turn off the switch to prevent it from being damaged, as explained below. In one embodiment, a second power switch (not shown) is provided in series with the switch 52 and the ground in a half-bridge configuration, where an output node is provided between the two power switches.

A gate driver 60, having an output node 62 and input nodes 64 and 66, is coupled to the other end of the resistor R2, so that the switch control signals may be applied to the control terminal of the switch 52. The input node 64 receives the switch control signals from an external source. The input node 66 receives output signals from the comparator 70.

The comparator 70 receives a reference signal V_(ref) and a sense signal I_(sen). The sense signal is received from the sense node 58, provided between the switch 52 and resistor R3 according to one embodiment of the present invention. The signal V_(ref) is used to determine whether or not the amounts of current outputted by the switch 52 exceed the circuit specification. In one embodiment, the signal I_(sen) may be converted to a signal V_(sen). The comparator then compares the two inputted signals and outputs a first signal, e.g., high voltage signal, if the signal V_(sen) is no more than the signal V_(ref). Otherwise, the comparator outputs a second signal, e.g., low voltage signal, that initiates an emergency turn-off of the switch 52.

FIG. 2 illustrates a schematic circuit diagram of the gate driver 60. The gate driver 60 includes a PMOS transistor 72 and an NMOS transistor 74 in series in a half-bridge configuration. The PMOS is coupled to a high voltage source Vcc, e.g., 15 volts, and the NMOS is coupled to a low voltage source DGND. An output node 76, provided between the two transistors, is coupled to the resistor R2 of the power module 50 and corresponds to the node 62 of FIG. 1. An inverter 78 is coupled to the control terminals of the transistors 72 and 74. An input 80 of the invertor receives an output signal from a signal generator 82. The signal generator is a circuit that outputs a high voltage signal to place the gate driver 60 in the turn-on state and a low voltage signal to place the gate driver 60 in the turn-off state. The signal generator is configured to output a low voltage signal if the comparator indicates that the signal V_(sen) is greater than the signal V_(ref) via the input node 66. In one embodiment, the signal generator 82 is an AND gate (not shown), but other logic gates or a combination thereof may be used in other embodiments.

For example, in operation, when a high input voltage signal is received at the input 80, a low voltage signal is outputted by the invertor, thereby turning on the PMOS transistor and turning off the NMOS transistor. As a result, a high input voltage is outputted as a switch control signal to the switch 52 to turn it on. However, if a low input voltage signal is received at the input 80, a high voltage signal is outputted to the gates of the transistors 72 and 74 to turn off the PMOS 72 and turn on the NMOS 74. Consequently, a low input voltage is outputted as a switch control signal to the power switch 52 to turn it off.

The gate driver 60 provides two conductive or electrical states: (1) a high output voltage, or (2) a low output voltage. Accordingly, the gate driver 60 only provides a hard turn-on or hard turn-off options. Although these two states are sufficient under normal operating conditions, a problem may result when the switch 52 experiences a sudden current spike. The switch would then be turned off hard according to the output signal from the comparator. This would generate a high transient energy that may damage the switch and related circuits.

Among other reasons, overheating and shorting of the of the inductance L1 is one reason for such a current spike. For example, if the circuit is shorted, the inductance L1 with an initial inductance of 100 μH may suddenly be provided with 0.1 μH, thereby generating a large current spike through the switch 52 since the current flow is inversely proportional to the inductance of the circuit. If this current spike is turned off suddenly with an emergency turn-off measure, a large transient voltage that may damage the switch and related circuits is generated. For example, the switch may be placed in an avalanche breakdown condition due to the high transient voltage.

Referring to FIG. 3A, in one embodiment, a power module 100 includes a power semiconductor switch or device 102, e.g., a power NMOSFET, having a first terminal coupled to a high voltage source, a second or control terminal coupled to a gate driver, and a third terminal coupled to a resistor R6 that is coupled to a low voltage source or ground. One end of a load 104, represented by an inductor L2 and a resistor R4, is coupled to the first terminal e.g., a drain electrode, of the switch 102. Another end of the load 104 is coupled to a high voltage source V_(bus). In one embodiment, the high voltage source V_(bus) provides about 140 volts to the load 104.

One end of a resistor R5 is coupled to the second terminal of the switch, and the other is coupled to the gate driver. The resistor R5 generally has a relatively low resistance, e.g., about 1 ohm, and is used to control the turn-on or turn-off speed of the switch. A sense node 106 is provided between the third terminal, e.g., a source electrode, of the switch and the resistor R6 to enable detection of any unusual current spike in the switch 102. In one embodiment, another switch (not shown) is provided in series with the switch 102 in a half-bridge configuration, wherein an output node is coupled between the two switches to output currents to an external circuit.

A gate driver 110 has an output node 112 and input nodes 114 and 116. The input node 114 receives control input signals, and the input node 116 receives enable and disable signals from a comparator 120. The output of the gate driver 110 is coupled to the resistor R5 to drive the switch 102 by applying switch drive signals to the control terminal of the switch 102.

In one embodiment, the gate driver 110 is configured to provide three conductive or electrical states (or tri-state outputs): (1) a turn-on state, (2) a turn-off state, and (3) a high impedance state. The gate driver is in the turn-on state if it outputs a high voltage to turn on the switch 102, and in the turn-off state if it outputs a low voltage to turn off the switch 102. If the switch is a PMOSFET, the gate driver is in the turn-on state if it outputs a low voltage to turn on the switch 102, and in the turn-off state if it outputs a high voltage to turn off the switch. The gate driver is in the high impedance state if the output node of the gate driver is provided with a high impedance.

Referring back to FIG. 3A, a first end of a pull-down resistor R7 is coupled to the node 112. The resistor R7 has a relatively large resistance value, e.g., 1,000 to 10,000 ohms. The second end of the resistor R7 is grounded. In one embodiment, the resistor R7 has about 3,000 ohms. The resistor R7 and the high impedance state of the gate driver 110 are used together to turn off the switch 102 slowly, i.e., to perform a soft turn-off, during an emergency turn-off operation, as explained in more detail later.

The comparator 120 receives a reference signal V_(ref) and a sense signal I_(sen). The sense signal is received from the node 106 and represents the amount of current flowing through the switch 102. The signal V_(ref) represents a maximum level of current or voltage that the switch 102 or related circuits are designed to handle safely. In one embodiment, the signal I_(sen) is converted to a signal V_(sen). The comparator then compares the V_(sen) and V_(ref) signals and outputs a first signal (enable signal) if the signal V_(sen) is no more than the signal V_(ref). Otherwise, the comparator outputs a second signal (disable signal) that initiates an emergency turn-off operation of the switch 102. In one embodiment, the enable signal is a high voltage signal, and the disable signal is a low voltage signal. The output of disable signal by the comparator 120 causes the gate driver 110 to enter into a high impedance state and overrides any signal received at the input node 114, according to one embodiment of the present invention.

In one embodiment, the gate driver 110, resistors R5 and R7, and comparator 120, collectively referred as a gate driving circuit assembly 103, are all provided within a single semiconductor chip 101.

Referring to FIG. 3B, in another embodiment, a power module 200 includes a power semiconductor switch or device 202, e.g., a power NMOSFET, a load 204, and a gate driving circuit assembly 203 including various circuits. The load 204 includes a resistor R4′ and an inductor L2′. A resistor R6′ is coupled to the switch 202. The gate circuit assembly 203 is provided within a single semiconductor chip according to one implementation. The circuit assembly 203 includes a gate driver 210, a comparator 220, and resistors R5′ and R7′. These correspond to the gate driver 110, the comparator 120, and the resistors R5 and R7 of the power module 100, respectively.

In addition, the power module 200 includes a transistor 207, provided between the resistor R7′ and the ground, to prevent current leakage at the output node of the gate driver 210. The transistor 207 is turned off when the gate driver 210 is activated A set-reset flip flop 205 is coupled to the output node of the comparator 220 to regulate the gate driver 210 and the transistor 207. A first output Q of the flip flop 205 is coupled to the gate of the transistor 207. A second output Q-bar of the flip flop 205 is coupled to one of the inputs 216 of the gate driver 210. The other input 214 of the gate driver 210 is coupled to an input of the flip flop 205 to reset it periodically. In one implementation, a differentiator 209 is coupled to the input 214 of the gate driver and the reset input of the flip flop 205 to provide a reset signal to the flip flop.

FIG. 4 illustrates a schematic circuit diagram of the gate driver 110 according to one embodiment of the present invention. The gate driver 110 includes a first or upper transistor 122 and a second or lower transistor 124 in series in a half-bridge configuration. A first terminal 126 of the upper transistor is coupled to a high voltage source Vcc of about 15 volts. A second or control terminal 128 of the upper transistor is coupled to an OR gate 130. A third terminal 132 of the upper transistor is coupled to a first terminal 134 of the lower transistor. A second terminal 136 of the lower transistor is coupled to an AND gate 138. A third terminal 140 of the lower transistor is grounded. An output node 142, corresponding to the node 112 of FIG. 3, is provided between the upper and lower transistors.

In one embodiment, the upper transistor is a P-type transistor, such as a PMOS transistor or PNP bipolar transistor. The lower transistor is an N-type transistor, such as an NMOS transistor or NPN bipolar transistor. The upper and lower transistors 122 and 124 are generally significantly smaller than the power switch 102 that is used to handle a high voltage, e.g., about 100 volts or more, and generate a large amount of current, e.g., about 10 amperes or more. In comparison, the upper and lower transistors 122 and 124 are configured to handle about 5-15 volts and generate about 2 amperes according to one embodiment of the present invention.

The gate driver 110 includes first and second inverters 142 and 144. An output of the first inverter 142 is coupled to an input of the OR gate 130. A first input of the inverter 142 is coupled to the node 116 to receive the enable or disable signal outputted by the comparator 120. An output of the second inverter 144 is coupled to a second input of the OR gate 130 and a first input of the AND gate 138. A second input of the AND gate 136 is coupled to the node 116 to receive the enable or disable signal.

In operation, the gate driver 110 is placed in the first conductive or turn-on state when the upper transistor 122 is on and the lower transistor 124 is off, thereby placing the node 142 at a high potential and causing electricity to flow to the control terminal of the power switch 102. The high resistance resister R7 is provided so that most of the electrical current from the gate driver 110 is applied to the second terminal rather than be diverted to the ground (see, FIG. 3).

In one embodiment, the gate driver is at the turn-on state when the node 116 receives an enable signal from the comparator 120 and the node 114 receives a high voltage signal. The comparator transmits an enable signal when the switch 102 is operating under normal conditions, i.e., there is no sharp current spike, so the signal V_(sen) is not greater than the signal V_(ref). In the present embodiment, the enable signal is represented by a high voltage signal, e.g., logic “1”, and the disable signal represented by a low voltage signal, e.g., logic “0”. In another embodiment, the enable signal may be a low voltage signal, and the disable signal may be a high voltage signal.

The gate driver is at the second conductive or tun-off state when the upper transistor is off and the lower transistor is on, thereby grounding the node 142. As a result, the control terminal of the power switch 102 is also quickly brought to a low potential or is grounded. The switch 102 is turned off as the voltage applied to the control terminal is decreased below the threshold voltage. In the present embodiment, the gate driver is at the turn-off state when the node 116 receives an enable signal from the comparator 120 and the node 114 receives a low voltage signal.

The gate driver is at the third conductive or high impedance state when both the upper and lower transistors are turned off. The gate driver is at the high impedance state if a disable signal is received at the node 116. The disable signal overrides the control signal received at the node 114. That is, the signal received at the node 114 does not effect the turn-on or turn-off characteristics of the upper and lower transistors when the disable signal is applied at the node 116.

The disable signal is outputted by the comparator if a sharp current spike in the switch 102 is detected. A large I_(sen) signal, representing the current spike, is applied to the comparator. The signal I_(sen) is converted to a signal V_(sen), where the V_(sen) is greater than V_(ref). The comparator, in turn, outputs a disable signal to the node 114 to place the gate driver at high impedance state. The charges applied to the control terminal of the switch are slowly dissipated via the resistor R7. As a result, the switch 102 undergoes a soft turn-off, thereby preventing generation of a large, harmful transient voltage spike which may damage the switch.

FIG. 5 illustrates a schematic circuit diagram of a gate driver 110′ according to another embodiment of the present invention. The gate driver 110′ is configured to prevent cross conduction in the driver's transistors. Unlike power switches which handle large amounts of currents, the cross conduction of transistors in the gate driver has not been seen as a serious problem. However, cross conduction is a more of concern at a higher frequency, i.e., 100 KHz or above. In fact, at 400 KHz or above, the cross conduction issues becomes a significant problem due to excessive current loss.

Accordingly, in high frequency applications, the gate driver 110′ includes first and second delay circuits 146 and 148. The first delay circuit 146 provided between an OR gate 130′ and a control terminal of an upper transistor 122′. The second delay circuit 148 is provided between an AND gate 138′ and a control terminal of a lower transistor 124′. The delay circuits are used to delay the propagation of the driver control signals to the control terminals of the upper and lower transistors. A dead time is provided between the turn-on time of the upper transistor and the turn-on time of the lower transistor to prevent cross conduction. In one embodiment, the delay circuits uses a plurality of inverters in series to obtain the desired signal delay, as explained in more detail in a concurrently filed patent application Ser. No. 10/136,844 entitled, “Efficient Gate Driver IC for Power Devices,” assigned to the present assignee, which is incorporated by reference herein for all purposes. Generally, the number, size, or type of inverters, or a combination thereof, may be used to obtain the appropriate delay propagation.

The above detailed descriptions are provided to illustrate specific embodiments of the present invention and are not intended to be limiting. Numerous modifications and variations within the scope of the present invention are possible. For example, the power switch 102 and other MOSFETs described above may be bipolar transistors in other embodiments of the present invention. Accordingly, the present invention is defined by the appended claims. 

What is claimed is:
 1. A power module, comprising: a power semiconductor device having a first terminal, a second terminal, and a third terminal, the second terminal being a control terminal to regulate flow of electricity between the first and third terminals; a gate driver having an output node coupled to the second terminal of the power device, the gate driver configured to output a first conductive state, a second conductive state, and a third conductive state; and a pull-down resistor having a first end and a second end, the first end of the pull-down resistor being coupled to the output node of the gate driver, wherein the gate driver includes: a first input node to receive a first input signal or a second input signal; and a second input node to receive an enable signal or a disable signal, wherein the output node of the gate driver is at the third conductive state if the disable signal is received at the second input node regardless of a signal received at the first input node, wherein the output node of the gate driver is at the first conductive state if the enable signal is received at the second input node and the first input signal is received at the first input node, wherein the output node of the gate driver is at the second conductive state if the enable signal is received at the second input node and the second input signal is received at the first input node.
 2. The power module of claim 1, wherein the gate driver further includes: a first transistor having a first terminal, a second terminal, and third terminals, the first terminal of the first transistor being coupled to a high voltage source; and a second transistor having a first terminal, a second terminal, and a third terminal, the first terminal of the second transistor coupled to the third terminal of the first transistor, wherein the output node of the gate driver is coupled to a node defined between the third terminal of the first transistor and the first terminal of the second transistor.
 3. The power module of claim 2, wherein the first transistor is a P-type transistor and the second transistor is an N-type transistor.
 4. The power module of claim 2, wherein the first conductive state of the gate driver applies a high potential to the second terminal of the power semiconductor device, the second conductive state of the gate driver applies a low potential to the second terminal of the power semiconductor device, and the third conductive state of the gate driver provides a high impedance state to the output node of the gate driver.
 5. The power module of claim 2, wherein the gate driver further includes: an OR gate having an output node, a first input node, and a second input node, the output node of the OR gate being coupled to the second terminal of the first transistor; and an AND gate having an output node, a first input node, and a second input node, the output node of the AND gate being coupled to the second terminal of the first transistor, the second input node of the AND gate being coupled to the second input node of the gate driver; a first inverter having an input node and an output node, the output node of the first inverter being coupled to the second input node of the OR gate and the first input node of the AND gate, the input node of the first inverter being coupled to the first input node of the gate driver to receive the first and second input signals; and a second inverter having an input node and an output node, the output node of the second inverter being coupled to the first input node of the OR gate, the input node of the second inverter being coupled to the second input node of the gate driver to receive the enable or disable signal.
 6. The power module of claim 5, further comprising: a comparator having an output node, a first input node, and a second input node, the output node being coupled to the second input node of the gate driver to provide the enable or disable signal according to signals received at the first and second input nodes of the comparator, wherein the gate driver, the comparator, and the pull-down resistor are all provided within a single semiconductor substrate.
 7. The power module of the claim 6, further comprising: a current sensor coupled to the third terminal of the power semiconductor device to output a sense signal according to an amount of current sensed by the current sensor, wherein the sense signal outputted by the current flow sensor is applied to the second input node of the comparator, wherein the first input node of the comparator receives a reference signal, wherein the comparator outputs the enable signal if the reference signal is greater than the sense signal and output the disable signal if the reference signal is less than the sense signal.
 8. The power module of claim 6, wherein the pull-down resistor is configured to slowly turn off the power semiconductor device by diverting the current applied to the second terminal of the power semiconductor device if the second input node of the gate driver receives the disable signal, thereby placing the gate driver at the third conductive state.
 9. The power module of claim 6, wherein the pull-down resistor has a resistance value of at least about 1,000 ohms.
 10. The power module of claim 6, wherein the pull-down resistor has a resistance value of at least about 3,000 ohms.
 11. The power module of claim 6, wherein the pull-down resistor has a resistance value of at least about 1,000 ohms and no more than about 10,000 ohms.
 12. A gate driver for a power semiconductor device, the driver comprising: an output node to apply a first electrical state, a second electrical state, and a third electrical state to the power semiconductor device; a first input node to receive a first input signal or a second input signal; and a second input node to receive an enable signal or a disable signal, wherein the output node of the gate driver is at the third electrical state if the disable signal is received at the second input node regardless of any signal received at the first input node, wherein the output node of the gate driver is at the first electrical state if the enable signal is received at the second input node and the first input signal is received at the first input node, wherein the output node of the gate driver is at the second electrical state if the enable signal is received at the second input node and the second input signal is received at the first input node.
 13. The gate driver of claim 12, further comprising: a first transistor having a first terminal, a second terminal, and a third terminal, the first terminal of the first transistor being coupled to a high voltage source; and a second transistor having a first terminal, a second terminal, and a third terminal, the first terminal of the second transistor coupled to the third terminal of the first transistor, wherein the output node of the gate driver is coupled to a node defined between the third terminal of the first transistor and the first terminal of the second transistor.
 14. The gate driver of claim 13, wherein the first transistor is a P-type transistor and the second transistor is an N-type transistor.
 15. The gate driver of claim 13, wherein the first electrical state of the gate driver applies a high potential to a control terminal of the power semiconductor device, the second electrical state of the gate driver applies a low potential to the control terminal of the power semiconductor device, and the third electrical state of the gate driver provides a high impedance site to the output node of the gate driver.
 16. The gate driver of claim 13, further comprising: an OR gate having an output node, a first input node, and a second input node, the output node of the OR gate being coupled to the second terminal of the first transistor; and an AND gate having an output node, a first input node, and a second input node, the output node of the AND gate being coupled to the second terminal of the first transistor, the second input node of the AND gate being coupled to the second input node of the gate driver; a first inverter having an input node and an output node, the output node of the first inverter being coupled to the second input node of the OR gate and the first input node of the AND gate, the input node of the first inverter being coupled to the first input node of the gate driver to receive the first or second input signal; and a second inverter having an input node and an output node, the output node of the second inverter being coupled to the first input node of the OR gate, the input node of the second inverter being coupled to the second input node of the gate driver to receive the enable or disable signal.
 17. The gate driver of claim 12, wherein the output node of the gate driver is coupled to a pull-down resistor.
 18. The power module of claim 12, wherein the pull-down resistor has a resistance value of at least about 1,000 ohms.
 19. The power module of claim 12, wherein the pull-down resistor has a resistance of at least about 3,000 ohms. 